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<TITLE>generate(), generate_n()</TITLE>
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<H2>generate(), generate_n()</H2>
<P><B>Module:</B>&nbsp;&nbsp;Standard C++ Library&nbsp;&nbsp;&nbsp;<B>Library:</B>&nbsp;&nbsp;<A HREF="2-9.html">Algorithms</A></P>

<PRE><HR><B><I>Function</I></B><HR></PRE>

<UL>
<LI><A HREF="#sec1">Local Index</A></LI>
<LI><A HREF="#sec2">Summary</A></LI>
<LI><A HREF="#sec3">Synopsis</A></LI>
<LI><A HREF="#sec4">Description</A></LI>
<LI><A HREF="#sec5">Complexity</A></LI>
<LI><A HREF="#sec6">Example</A></LI>
<LI><A HREF="#sec7">See Also</A></LI>
<LI><A HREF="#sec8">Standards Conformance</A></LI>
</UL>
<A NAME="sec1"><H3>Local Index</H3></A>
No Entries
<A NAME="sec2"><H3>Summary</H3></A>
<P>Algorithm that assigns each element in a range a value produced by repeated application of the given function object</P>
<A NAME="sec3"><H3>Synopsis</H3></A>

<PRE>#include &lt;algorithm&gt;

namespace std {
  template &lt;class ForwardIterator, class Generator&gt;
  void generate(ForwardIterator start, ForwardIterator finish,
                Generator gen);

  template &lt;class OutputIterator, class Size, class Generator&gt;
  void generate_n(OutputIterator start, Size n,
                  Generator gen);
}
</PRE>
<A NAME="sec4"><H3>Description</H3></A>
<P>A value-generator function returns a value each time it is invoked. The algorithms <SAMP>generate()</SAMP> and <SAMP><A HREF="generate.html">generate_n()</A></SAMP> assign each element in the sequence <SAMP>[start, finish)</SAMP> or <SAMP>[start, start + n) </SAMP>the return value of the generator function <SAMP>gen()</SAMP>. The function <SAMP>gen()</SAMP> takes no arguments. (<SAMP>gen()</SAMP> can be a function or a class with an <SAMP>operator()</SAMP> defined that takes no arguments.)</P>
<P><SAMP><A HREF="generate.html">generate_n()</A></SAMP> assumes that all iterators in the range <SAMP>[start, start + n]</SAMP> are dereferenceable, unless <SAMP>start</SAMP> is an insert iterator.</P>
<A NAME="sec5"><H3>Complexity</H3></A>
<P>The <SAMP>generate()</SAMP> and <SAMP><A HREF="generate.html">generate_n()</A></SAMP> algorithms invoke <SAMP>gen()</SAMP> and assign its return value exactly <SAMP>finish - start</SAMP> (or <SAMP>n</SAMP>) times.</P>
<A NAME="sec6"><H3>Example</H3></A>

<UL><PRE>//
// generate.cpp
//

#include &lt;algorithm&gt;    // for generate, generate_n
#include &lt;iostream&gt;     // for cout, endl
#include &lt;vector&gt;       // for vector



// Value generator simply doubles the current value 
// and returns it.
template &lt;class T&gt;
class generator
{
    T val_;
public:
    generator(const T &amp;val) : val_ (val) { }
    T operator()() {
        return val_ += val_;
    }
};


int main ()
{
    // Typedef for convenience.
    typedef std::vector&lt;short, 
                        std::allocator&lt;short&gt; &gt; vector;

    vector::value_type arr[4] = { 1, 2, 3, 4 };

    // Set up two vectors.
    vector v1(arr, arr + sizeof arr / sizeof *arr);
    vector v2 = v1;

    // Set up one empty vector.
    vector v3;

    // Create a generator function object.
    generator&lt;vector::value_type&gt; gen(1);

    // Generate values for all of v1.
    std::generate(v1.begin(), v1.end(), gen);

    // Generate values for first 3 of v2.
    std::generate_n(v2.begin(), 3, gen);

    // Use back_insert_iterator to generate 5 values for v3.
    std::generate_n(std::back_inserter(v3), 5, gen);

    // Copy all three to cout.
    std::ostream_iterator&lt;vector::value_type, char,
             std::char_traits&lt;char&gt; &gt; out(std::cout, " ");

    std::copy(v1.begin(), v1.end(), out);
    std::cout &lt;&lt; std::endl;

    std::copy(v2.begin(), v2.end(), out);
    std::cout &lt;&lt; std::endl;

    std::copy(v3.begin(), v3.end(), out);
    std::cout &lt;&lt; std::endl;

    // Generate 3 values into cout.
    std::generate_n(out, 3, gen);
    std::cout &lt;&lt; std::endl;

    return 0;
}


Program Output:
</PRE></UL>
<UL><PRE>2 4 8 16 
2 4 8 4 
2 4 8 16 32 
2 4 8 
</PRE></UL>
<A NAME="sec7"><H3>See Also</H3></A>
<P><A HREF="functionobjects.html">Function Objects</A></P>
<A NAME="sec8"><H3>Standards Conformance</H3></A>
<P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 25.2.6</I></P>

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